1. Field of the Invention
The present invention relates to reciprocating engines and piston designs, particularly in the automotive field. More specifically, the present invention pertains to a high efficiency piston that reduces viscous drag and mechanical losses as it translates through its range of motion from bottom dead center (BDC) to top dead center (TDC) within a reciprocating engine.
Reciprocating engines utilize a piston-cylinder configuration to capture the power of expanding gases to create work in the form of translation of the piston within the cylinder, which in turn rotates a crank to power a vehicle, operate an electrical generator or perform a duty unto which rotating mechanical power is a motive input. An engine piston is positioned within a cylinder with minimal clearance and tight tolerancing, wherein the interface between the piston and cylinder bore is heavily lubricated via the continual application of oil along the cylinder walls during operation. Proper oiling of the cylinder during engine operation is critical to controlling and preventing excessive thermal load build-up, frictional losses and even engine seizure. Typical piston-cylinder devices are comprised of a metallic structure, which expands readily under thermal load. Intense heat due to the ignition of the engine fuel-air mixture within the cylinder conducts through the walls of both the piston and cylinder, resulting in a large thermal flux and the relative expansion of components within the engine. To prevent these components from expanding excessively and clashing with one another, proper lubrication and engine design is critical, and further reduces frictional wear and improves engine longevity.
The interface between the piston and cylinder of a reciprocating engine is a piston ring device. Piston rings are peripherally mounted about the outer diameter of the piston head and are positioned within grooves therealong. The piston rings are generally semi-circular rings that are allowed to expand under thermal load without creating an interference, while their positioning on the cylinder head serves two primary functions. The first of which is to prevent the fuel-air mixture within the piston from bypassing the piston head during expansion, and thus retaining proper compression within the cylinder and allowing the expanding gases to convert its kinetic energy into piston work as designed. The second function of the piston rings is to skim oil from the cylinder bore as it translates therein. Oil is sprayed along the piston interior bore to facilitate reduced friction and heat, and thus reduced wear. The piston ring leave a lubricating oil film of a few micrometers thick on the bore surface, so as the piston descends along its path within the cylinder, the thin film provides adequate lubrication, heat dissipation and thus reduced wear on the engine. Piston rings can thus be differentiated as either compression rings and oil control rings, wherein their moniker denotes their function. Most reciprocating engines employ a plurality of piston rings for the foregoing functions, wherein one or a plurality of a single piston ring type may be deployed for improved function and thus improved compression sealing and oil control. Dual compression rings may prevent undesired loss of compression, while dual oil control rings prevent build-up of oil along the bore if the oil is less than uniform, and further prevent oil from entering the fuel-air mixture and burning.
While piston rings may facilitate a thin film of lubrication, there still exits friction between the piston and the cylinder during operation, in the form of viscous drag (fluid friction) and mechanical friction. The present invention relates to a piston design that is adapted to provide improved mechanical efficiency, smoother operation of the engine and lower emissions as the life of the engine increases. Typical pistons employ a cylindrical head and a similarly cylindrical piston skirt, which extends over the connection to the piston rod. As such engines increase in temperature and even begin to overheat (if adequate cooling is not provided), expansion under thermal load occurs, leading to increased friction between the piston and cylinder bore and potentially a seizure of the engine itself, as the friction between the components becomes too great or they fuse together under intense heat.
The present invention is specifically related to a piston shape that comprises a cylindrical piston head, wherein the piston skirt is a tapered shape having an inwardly concave central portion before terminating at a lower portion of equal radius as the upper piston head. This shape allows the piston to dissipate heat through the lower portion and reduces expansion under considerable thermal load, while the concave shape allows for material growth without risking seizure of the engine. Current piston designs have considerably high mechanical losses with regard to the energy wasted from the expanding gases in the form of mechanical friction and oil drag. The present invention is a more efficient component that not only reduces these power robbing elements, but also decreases the amount of fuel needed to efficiently operate the engine, while also increasing the longevity of any engine equipped with the present piston configuration. Hydrocarbon emissions are also reduced, as the piston rings are more effective at sealing the combustion chamber and less oil is burned during an engine cycle. The present invention is designed to provide an engine that runs quiter, cooler, and still prevents excessive oil consumption in excessively high mileage vehicles.
2. Description of the Prior Art
Several devices have been disclosed in the prior art that relate to piston designs and those that relate to improved mechanical efficiency. Several devices have been patented or disclosed in published patent applications. These devices have familiar design elements for the purposes of providing a new piston configuration for a reciprocating engine; however none are provided in the configuration as disclosed in the present invention. The disclosures deemed most relevant to the present invention are described below.
Specifically, U.S. Pat. No. 6,206,248 to Popp, U.S. Pat. No. 4,809,591 to Rhodes, and U.S. Pat. No. 4,648,309 to Schellmann all disclose pistons having a particular shape so as to reduce friction and wear on the inner bore of a cylinder. These devices include piston skirts that comprise inwardly shaped profiles, but fail to disclose a concave shape having a recessed pin boss and a lower oil control ring to facilitate reduced friction and improved lubrication throughout the engine cycle. These prior art devices are well adapted for their particular purpose, but fail to disclose a piston having an inwardly concave central portion with a first and second oil control ring on either side of the concave portion.
The present invention provides a new and improved piston shape that reduces potential contact area between the central portion of the piston and the cylinder bore, while also improving lubrication in the form of a plurality of oil control rings surrounding the inwardly concave central portion of the piston. The result is reduced friction, reduced mechanical losses, increased heat dissipation and a smoother running engine that can reduce wear in high mileage engines. It is submitted that the present invention is substantially divergent in design elements from the prior art, and consequently it is clear that there is a need in the art for an improvement to existing devices. In this regard the instant invention substantially fulfills these needs.